it just show
by Admin -
without date
I think this is because of a strange logic when to show the date: see plone.app.layout/plone/app/layout/viewlets/document_byline.pt at master · plone/plone.app.layout · GitHub
There is the view/pub_date which checks for the setting in the security config display_publication_date_in_byline and if an effective date is set at all.
And there's the view/show_modification_date which checks for an available effective_date and if the effective_date is earlier than the modification_date... so this is only shown, if your item is published and if its modified after this publication date ... this makes no sense to me. If I want to show the date it should be shown without this logical salto mortale ...
There's also a issue about that: Inconsistency in document byline · Issue #330 · plone/plone.app.layout · GitHub